The present invention relates generally to a swing-arm type vehicle suspension, such as a trailing arm or semi-trailing arm suspension, which can provide both good drivability and good cornering stability. More particularly, the invention relates to a swing-arm type suspension which prevents occurrence of toe-out change in compliance or roll steering, especially in roll steering which causes the camber to change in the positive direction.
It is well known that good drivability and higher cornering force can be obtained by providing weak understeer characteristics for a vehicle suspension. One of the essential features for providing understeer characteristics is to keep the toe angle in the toe-in direction when subjected to a cornering moment. Otherwise, toe-out change may provide an oversteer characteristic for the vehicle suspension which can adversely affect drivability and cornering stability. This toe-out change in the vehicle suspension may occur in compliance steering or roll steering as a result of changes of the suspension geometry and deformation of the suspension bushings.
In order to prevent the occurance of toe-out change in a vehicle suspension, European Published Application No. 0070025, filed by the assignee of the present application, discloses a swing-arm type suspension having a laterally extending assist link for resisting external lateral forces.
The present invention is generally directed to an improvement of the foregoing swing-arm type suspension described in Published European Application No. 0070025. More particularly, the invention concerns a swing-arm type suspension which eliminates the tendency for toe-out change to occur in roll steering which brings the vehicle suspension into positive camber. This camber change occurs as a suspension arm in the swing-arm suspension is rotated about an axis which is inclined with respect to the longitudinal axis of the vehicle, which rotational axis of the suspension arm will be referred to hereinafter as the "camber axis". In the swing-arm type suspension, especially in a trailing arm or semi-trailing arm suspension, the rotation of the suspension arm about the camber axis affects the toe angle and causes toe angle change due to lateral displacement of the suspension arm. If the axis of a wheel spindle mounted on the suspension arm is displaced upwardly and rearwardly by the rotation of the suspension arm about camber axis, toe-out change will occur. If the lateral displacement of the wheel spindle upon the occurrence of positive camber changes can be prevented, toe-out change can be prevented.
On the other hand, the toe angle does not change even though camber changes, when the camber axis lies parallel to the rolling direction of the road wheel. Therefore, to prevent the road wheel from changing toe angle, the camber axis should be as nearly parallel as possible to the rolling direction of the road wheel. In a trailing arm or semi-trailing arm suspension, the longitudinal central axis of the suspension arm is generally shifted or inclined outwardly toward the rear with respect to the transverse axis of the road wheel so that a relatively short spindle may be used to mount the road wheel. It is impractical to shift the rear end of the suspension arm inwardly so that the suspension arm has a camber axis substantially parallel to the rolling direction of the road wheel, since this would require a longer spindle which, to have enough strength, would undesirably increase the suspension arm weight. Therefore, it is impractical provide a suspension arm which is substantially parallel to the rolling direction of the road wheel.
Unless otherwise specified, references herein to the laterally outward and laterally inward directions are intended to refer to the directions away from, or toward, the longitudinal axis of the vehicle, respectively.
The term "rolling direction" of a road wheel is intended to refer to the direction established by a horizontal line through the center of the wheel perpendicular to the rotational axis of the wheel.